Accumulator system



l Nv. '1, 1932. J. w. STEVENS ET AL ACCUMULATOR SYSTEM Filed Jan. 15, 1931 Patented Nov. l, 1932 UNITED STATES YPATENT OFFICE TERRY W. STEVENS .AND WILLIAM H. KENETY, OF CLOQIET, MINNESOTA, ASSIGNORS T0 CHEHIPULP PROCESS INC., OF WATERTOWN, NE\V YORK, A CORPORATION OF NEW Yonx Application led January 15, 1931.

The present invention relates to processes for cooking wood and other cellulosic material for the formation of pulp. and it. has particular reference to the preliminary operations g in the sulphite process, to the relief of the digester, to the utilization of the heat in the materials relieved, to the recovery of the materials, and to the combination of such utilization and recovery with said preliminary operations In the cooking of Wood by the sulphite process, using any of the suitable bases, of which calcium, magnesium and sodium are commonly known, it is necessary to use an 1l acid sulphite and an excess of free sulphur.-

ous acid dissolved in the cooking liquor. The excess acid usually varies in amount. y It it not constant, because itis held very loosely in the liquor, and increased heat and de- Ncreased pressure both cause it to be discharged from Asolution in the liquor. It is therefore customary to charge a digester with a cooking liquor in which the free acid content is very high. The tendency of the llsubsequent heating to drive it off is somewhat balanced by the tendency of the increasing pressure to prevent its escape.- In the present practice of the sulphite process Where steam is injected into the liquor there is an escape of much free acid from the process, and this is accom anied by discharge of a 'quantity of the coo ing liquor. Vents or relief lines suitably placed about the digester have valved controls to regulate the escape of such material and to control the pressure.

It is uite desirable to have all the chips in the digester covered with the cooking liquor, and accordingly the digester is quite full. The injection of the heating steam 40 causes condensation, and in order to accommodate the increased volume of water resulting from such condensation a portion of the liquor is released. It is customary to bleed liquor from the digester at a rate which will 4l compensate for the water being added. This liquor and the acid which is also set free are greatest in amount at the beginning of the heating operation and in the early part of the cook, but nevertheless a'substantial amount 50 of gas and vapor escape during the entire ACCUMLATOR ,SYSTEM Serial No. 508,911.

cook. The material tirst removed by relief is of greater purity than that which is later relieved. for after the cooking has proceeded there are present in the liquor various impurities removed from the chips, such as pitch. lignins, dissolved resins. oils. organic' acids, etc.

In the preliminary operations of the sulpliite process the liquor is usually introduced so that heating begins at a tenqierature of about T00 C., and cooking action does' not begin until three or four hours after the heating commences. This heating period involves the introduction of much water as steam, and requires the displacement of an -tion. `Absorption of the free acid gas at atmosphericy and at great pressures has been proposed. but there are disadvantages to these operations. At atmospheric pressure the temperature which can be attained is limited. At higher pressures the back pressure increases and a constant and uniform relief cannot be maintained. Furthermore. the introduction of the relief materials into the new liquors contaminates them with the impurities which they carry. and there is thus an accunmlation of detrimental materials which gives low grade pulp in. subsequentcooking operations with such liquor.

In our copending joint application Serial No. 249.845. filed January 2i', IQQS. there is described an accumulator system for saving heat and chemicals in operation of an acid sulphite process. In that application there is disclosed an accumulator into which relief gasand liquor are discharged against a back pressure for absorption by. and the preheating of, fresh cooking liquor contained in the accumulator. A system is disclosed for diverting the liquor from direct discharge into the accumulator to passage through heat eX- change apparatus, so that heat from relief material is given up to the liquor in the accumulator.

The present invention relates to improvements 1n the process and apparatus of said prior application.

One object of the present invention is the provision of automatic pressure controlled means for regulatin the diversion of relief material of several igesters from discharge into the accumulator to other means of disposal.

Another object is the operation of a plurality of digesters simultaneously in combination with a single accumulator, especially to permit each digester to operate at any pres sure, or at any stage of a cooking process, without interference by reason of a different condition prevailing in any other digester.

A further object of the invention is the provision of an accumulator in combination with a plurality of digesters in order to permit prolonging the period of direct discharge of relief material, and in order to heat the accumulator contents simultaneously by direct discharge and by heat transfer methods,

Various other and ancillary objects and advantages of the invention will be apparent from the following description of the proces s and the apparatus which is hereinafter given as an example of the invention as it is applied specifically to the sulphite process uslng a calcium base, and as shown on the accompanying drawing.

In the drawing:

Fig. shows a digester system, a separator for a digester, an accumulator, and various connections for suitable operation of the proc- GSS.

Fig. 2 shows a modification having a common eat exchanger for the several digesters. In order to explain the invention and to enable others to comprehend the scope of the appended claims a detailed reference to the apparatus and to its operation is given.

Three digesters are shown, but it is understood that more or less may be employed in practiclng this invention. They are designated 10, 11 and 12, each being roughly fifty feet 1n height, and about fifteen feet in diameter. Each digester may be fitted at the bot- ,tom with connections for a blow line 13, a

steam injection line 14, and a liquor supply l1ne 15. Suitable valves are provided in A these lines for example, the valve 16 in the blow 1ine,'the valve 17 in the steam line, and valve 1.8 in the liquor supply line. Various rehef lmes, as generally employed in the art, are connected to the digester, such as the top r e11ef line 19 with a valve 20, and a side relief line 21 with. a valve 22.

The two relief lines unite beyond their valves into line 23 leading into a separator for the separation of liquid and gas and/or vapor. In the present instance a horizontal cylindrical tank about eight feet long by two feet in diameter is designated 24, with line 23 entering one end at the center. The bottom of the tank is connected for drainage to a line 25 with valve 26. This drainage line may lead to a waste receiver or to the usual liquor cooler used for sulphiting apparatus, or to any other means for disposal of the separator liquor. Liquid, or gas and vapor which may collect above a liquid level in the separator, is conducted through line 27 to suitable means which will utilize the chemical and heat value in accordance with the present invention. The separator system is no necessary part of the present invention, and the relief line 27 from digester 10 may be an extension of the line 23. Digesters 11 and 12 have respectively relief lines 28 and 29.

An accumulator 30 is4 provided which is preferably large enough to hold about one and one-half times the amount of liquor necessary to charge a digester for cooking. Tt may be placed at an level with reference to the digester, but prefer to elevate it. The upper level creates a static head opposing the pressureof relief material and this head must be considered in the design and operation of the system. The accumulator is preferably provided as a lined pressure tank of steel. It has a valved vent 31 at the top from which air or gas therein may be relieved when required, for example, by discharge into some portion of the gas `re covery or absorption system. There is a liquid-carrying line 32 and valvel 33 for filling and emptying the accumulator. The line connects at 34 to a raw liquor feed main 35 which leads to the lines 15 for each digester, and to a valved line 36 connecting with the pressure side of a pump 37 which supplies fresh raw liquor by drawing a supply (not shown) through a feed line 38.

Each digester system may be similarly constructed in its relation to the accumulator. The relief lines 27, 28 and 29, exemplified by line 27, divide forming a line which discharges directly into the accumulator and a line which passes through heat exchange means within the accumulator, according to the invention of the applicant Kenety described in a copending application Serial No. 509,299, iiled January 17, 1931.

When iiow of relief material which is llO discharging into the digester begins to cease l or to become too slow because of back pressureV from the accumulator, an automatic valve, set for a certain pressure opens the line through the heatexchanger and permits relief of the digester to continue regardless of the back pressure.

Suitable structure for such operation is represented for all the digesters and is described with reference to t-he digester relief line 27. Relief line 27 enters a Y connector 40 which creates discharge branch 41 and heat exchange branch 42. A shut-off valve 43 and a check valve 44 preventing back flow from the accumulator may be placed in the discharge line 41. A pressure operated valve, such as a pop valve 45, is placed in line 42 and is adapted to open at a set pres sure Which may be varied at will. The line opens for passage of relief through heat exchange means 46 inside the accumulator, which carries the liquor into waste'line 47.

This line may be connected to other recoverysystems, for example, another accumulator, associated with the illustrated accumulator' in the manner described in a copending application of the applicant Kenety, Serial No. 509,299, filed January 17,1931.

The systems for digesters- 11 and 12 have respectively the open discharge lines 50 and 51, the check valves 52 and 53, the cut off valves 54 and 55, the pop valves 56 and 57, the heat exchangers 58 and 59 and the waste lines 48 and 49.

A modification is shown in Fig. 2 in which the several heat exchangers of Fig. 1 are united into a single heat exchanger. An accumulator 60 has therein a single heat exchanger 61. Several digesters have the relief lines 62, 63 and 64, each of Which divides into two branches. The respective branches 65, 66 and 67 have pressure operated relief valves 68 therein and beyond the valves combine into a single line 69 which is connected to the heat exchanger 61. Material iiows from the heat exchanger through waste line 70. The other branches 71, 72 and 7 3 enter the accumulator and discharge thereinto.

Check valves 74 prevent back flow from the accumulator to the digesters. Cut off valves 75 are yalso placed in the lines.

In the event that the relief material from the heat exchanging passage through the accumulator is to be selectively recovered or treated the several heat exchangers of Fig. 1 are preferred. Where no particular use is made of such material the single heat exchanger of Fig. 2 may be used. However, I prefer to use the several ones, and in practice have them arranged so that they are interchangeable in their relation to the several digesters.

In operation, fresh cooking liquor, which may be warm and under pressure, is placed in the accumulator to be further heated under pressure and enriched With relief gas. A digester, for example 10, which, We assume has just started into operation (and which may have been charged with hot rich liquor previously drawn from the accumulator) is heated by introducing steam. Side and top relief material in pipe line 27 is passed into the 'accumulator by way of discharge line 41. The check valve 44 prevents pressure in the accumulator causing a flow into the digester. It will be understood that the static head controls the pressure at which relief begins, and that the less the static head, the lower such pressure may be.

As heating or cooking continues the pressure in the 'accumulator increases so that back pressure therein may equal the relief pressure. This Will prevent relief and may effectively stop flow in line 41. In consequence the pressure in the digester 10 'will begin to rise. When it reaches a predetermined point, which may be before or after the flow in line 41 stops, the pop valve 44 opens and permits passage of relief material to take place through heat exchanger 46. As pressure in the digester is reduced as a result of the flow through the heat exchanger, it may reach a point where the pop valve closes. lIhus the setting of the pop .valve effectively and delicately controls the pressure of operation of the digester, keeping it very constant, automatically.

The pressure at which the valve operates may be xed or varied at will to control the relief and the digester pressure, and it may be set to cause the relief to shift from direct discharge into the accumulator to flow through the heat exchanger at a point where the impurities in the relief material become detrimental or injurious to the quality of liquor being prepared in the accumulator. During the heating period for la cooking operation,.and in the early stages of cooking the relief material is not highly contaminated with undesirable impurities, and its recovery by absorption in the accumulator is highly desirable.

Other digesters may be similarly operated. A bank of digesters are usually charged and cooked in a sequence, 'and the relief from a plurality of them may be so controlled that when one has its direct discharge into the accumulator cut off, the other begins to discharge into the accumulator, and so on in sequence. However, after the first filling of the accumulator with fresh liquor the rst digester creates an increased pressure in the accumulator, against which the next digester must discharge. It is therefore desirable to ing period of a cook prior to cooking, and lessens the amount of heat and chemicals lost by relief, thus shortening the total time ofl the cook, and making it more economically accomplished.

Any digester may be iilled from the accumulator While any other digester is being discharged into the accumulator. One charge in the accumulator may be enriched and heated by relief from several digesters, and it may be heated simultaneously by direct discharge 'and by transfer methods.

Various changes may be made in the apparatus and in operation, as Will be apparent to those skilled in the art. The invention is not to be considered as limited to the process 'and apparatusherein illustrated and described, but contemplates such other forms and variations as fall Within the scope of the appended claims.

We claim:

1. Apparatus for recovering relief material and the heat thereof from the bleeding of heated pressure cookers which comprises a plurality of pressure digesters, a pressure vessel for holding liquid to be heated, a pipe connection from each digester discharging into said pressure vessel, a valve in each of said pipe connections, a heat exchanger in said vessel for each digester, a pipe connection from each heat exchanger to a digester, and a. pressure operated valve in each of said last named pipe connections adapted to open the. pipe line at a predetermined pressure from the digester.

2. Apparatus for recovering relief material and the heat thereof from the bleeding of heated pressure cookers which comprises a plurality of pressure digesters, a pressure vessel for holding liquid to be heated, a pipe connection from each digest-er discharging into said vessel, heat exchanging means in said vessel,.pipe connections from said means to each of said digesters, and a pressure operated valve in each of said last named pipe connections adapted to open said pipe connection at a predetermined pressure from the `connected digester.

3. Apparatus for recovering relief material and the heat thereof from the bleeding of heated pressure cookers which comprises a plurality of pressure digesters, a pressure vessel for holding liquid to be heated, a pipe connection from each digester discharging into said vessel, a valve in each pipe connection for preventing back How tov the digester, heat exchanging means in said vessel, pipe connections from said means to each of said digesters, and a pressure operated valve in each of said last named pipe connections adapted to open said pipe connection at a predetermined pressure from the connected digester.

4. Apparatus for recovering relief material and the heat thereof from the bleeding of heated pressure cookers which comprises a plurality of pressure digesters, a pressure vessel for holding liquid to be heated, a pipe connection from each digester discharging into said vessel, a' valve in each pipe connection for preventing back iiow to the digester, heat exchanging means in said vessel, pipe connections from said means to each of .said digesters, and a pressure operated valve in each of said last named pipe connections adapted to open said pipe connection at a predetermined pressure from the connected digester, said pressure valves being set for sequential opening operations in accordance with the pressures prevalent in the digesters.

5. Apparatus for recovering relief material and the heat thereof from the bleeding of heated pressure'cookers Which comprises a plurality of pressure digesters, a pressure vessel for holding liquid to be heated, a pipe connection from each digester discharging into said vessel, a heat exchanger' in said vessel, pipe connections from each digester to said heat exchanger, and a pressure operated valve in each of said last named pipe connections adapted to open said pipe connection at a predetermined pressure from the connected digester.

6. Apparatus for recovering relief material and the heat thereof from the bleeding of heated pressure cookers which comprises a plurality of pressure digesters, a pressure vessel for holding liquid to be heated, a pipe connection from each digester discharging into said pressure vessel, a valve in each of said pipe connections, a heat exchanger in said vessel, a pipe connection from each digester to said heat exchanger, and a pressure operated valve in each of said last named pipe connections adapted to open said pipe line at a predetermined pressure from the connected digester.

7. Apparatus for recovering relief material from the bleedingof heated pressure cookers which comprises a plurality of di gesters, a pressure vessel for holding liquid, a pipe connection from each digester discharging into said vessel, a second pipe connection from each digester for carrying ofi' relief material therefor` and a pressure operated valve in said connection adapted to open said connection at a predetermined pressure in the digcstcr and to close said connection below said pressure.

8. Apparatus for recovering relief material from the bleeding of heated pressure cookers which vcomprises a plurality of digesters, a pressure vessel for holding liquid` a pipe connection from each digester discharging into said vessel, a valv(` in each of said pipe connections to prevent back fiov.Y of material from the vessel to the digester. a second pipe connection from each digesier for carrying off relief material then-freni. and a pressure operated valve in said connecfor passage into a 'heat exchanger associated with said confined liquor,-while continuing direct discharge of relief material from the second digesterinto the confined liquor.

` In witness whereof we have hereunto affixed our signatures.

JERRY W. STEVENS. W'ILLIAM H. KENETY. 

